Wear course for pavements



April@ 2, l929. L, R, MaCKENZlE 31,3@79939 WEAR COURSE FOR PAV'EMENTSFiled Aug. 6, 1928 2 She'e'S-Shee l WEAR COURSE FOR PAVEMENTS Filed Aug.6, 1928 2 Sheets-Sheet 2 Patented Apr. 2, i929..

Laon n. MACKENZIE, or Das MOINES, iowa.

WE COURSE FOR PAYMENTS;

Application led August 6,

has to do with a wear 'course My invention of the asphaltor bltuminousfor a pavement type. It is my purpose to provide a payement soconstructed by simple and economical methods that the normal movement ofthc body of material Awithin itself is ,prevented or eliminated.

It is also my purpose to provide a slmple and inexpensive method ofmaking such a pavement.` 4 u With these and other objects 1n view, myinvention consists in the` arrangement' and' construction of thepavement and the method of making the same as set forth in the'followingdescription defined in my clalms, and illustrated in the accompanyingdrawings, in which: i

Figure 1 shows a perspective view, partly in section, of the lowercourse, re-inforcmg and upper course of my pavement before they areplaced in proper superposed position. n

Figure 2 shows a vertical, sectional view of the pavement, illustratingit before and aft/er rolling. U

Figure 3 is a perspective view of a piece of the mesh re-inforcing. D

Figure 4 is a perspective kview, partly 1n section, of the pavement,illustrating the relative arrangement of courses and re-inforcing. y

Figure 5 is a vertical, sectional view of the pavement made in one way,before rolhng.

Figure 6 is a similar view of the same pavement after it is rolled.

Figure 7 is a vertical, sectional view of the pavement laid in aslightly different way, before rolling; and

Figure 8 is a similar view of the same, after rolling. l

Highway engineers recognize generally that the sheet asphalt type makesperhaps the most satisfactory top'or wearing course for a pavementsurface. The asphaltic top or wearing course is laid upon asuitablebase, such as rolled gravel; concrete, bituminous mixture, lWater-boundmacadam and so on.A n

Heretofore the use of sheet asphalt forthe wearing course of thepavement has been subject to recognized diiiculties and defects.

1928. Serial No, 297,633.

lt has been extremely difficult to prevent the somewhat plastic asphaltor bituminous layer from shifting or rolling to form high and low spots,which causerough traic surface conditions.

lThe use of motor vehicles has greatly increased these diHicult-ies. TheeHect of stopping and starting of motor vehicles and general motorvehicle trac tends to pull or push the upper portion of the asphalt coator surface, forming the ridges, humps and hollows which are so wellknown.

It is Well known that during the summer months when the air temperatureis quite ,highl that asphaltic materials, from which the wear course ofa pavement is ordinarily l formed, are subjected to easy displacementVdue to traffic upon the wear course.

The asphaltic materials during the high f temperature f the summermonths are com-y paratively soft or pliable and due to traffic thereonare lvery vquickly and easily displaced.

t is further well known that asphaltic materials have a greaterafinityfor heat and the retention of the same. It thus follows that the heatwhich is absorbed within the pavement will give to the pavement atemperature greater or higher than the air temperature.

The degree of heat Within the pavement is retained for a considerablelength of time after the suns heat rays have been absorbed,

and it is my object to provide a pavement that will eliminate themovement of the. asphaltic naterial within itself.

When the surface material does move until the surface course is ofdifferent thicknesses at different places, the wear and deteriorationsubsequently increase rapidly. Small depressions and then holes developin the surface, which are enlaroed by continuous pushing, shoving andtraffc impact and traction, resulting in the formation of morehumps,ridges posure of the base in places. When the holes are so formed or thebase exposed, water works into the holes and low pla/ces, seeps underthe surface sheet, and increases the rapidity of disintegration of theentire pavand hollows and ultimate ex- Y which could be pushed about andwould thus move with relation to the lower portion, even though thelower portion might be fixed to a base.

ll have found that there is in any bituminous pavement course, what maybe called an axis of movement vwithin itself. Even though the lower'part of the course may be anchored to the base, the upper part of theplastic material will move with relation to the lower part. 0napproximately ansinch in thickness of rolled surface asphalt undertraffic, this axisV of movement is scarcely perceptible, atapproximately an inch and a half it becomes apparent, and vover twoinches 1t is quite noticeable.

'llhe various methods andstructures which have been adopted foranchoring the asphaltic top'cour'se to the base course have thereforebeen unsatisfactory because they did not prevent the rolling or movementof the upper part of the asphaltic course within itself, and theresultant wavy formation causing a rough traffic surface unsatisfactoryfor trafhc and leading to morerapid deterioration.

Under present trafc conditions, a bituminous course, which is thinenough tofeliminate this normal movement of the material within itself,is too thin for practical use.

A relatively thin asphaltic or bituminous course is not sufficient forpractical purposes, due to the fact that it will not stand weather andtralic conditions to which it is generally subjected. Such asphalticcourses usually have from seven to ten percent of pure' asphaltic -orbituminous cement, containing volatile oils. Hence, when a shallow bodyof asphalt or bituminous top mixture is exposed to the sun, there is notsufficient depth or body to the mixture to retain its vitality andWearing qualities for a proper length of time. 'llhe hot summer sun intime will draw out the volatile oils, and there remains a hard cokelikesubstance, which quickly disintegrates and pulverizes under traffic.

llt therefore follows that where there is not Asulhcient depth to theasphalt wearing course imanes "give long life to the pavement, and ifthe depth is sufficiently increased to retain the chemical ingredientsessential for prolongation of the life of the material, the axis of vmovement hvitliin itself is far enough below the top of the surface topermitmovement above that axis with the resultant rolling and wave-likeformation, which is highly objectionable. i

lt is obvious that anchoring the top course to the base will not meetthese objections.

. Efforts have been made by the admixture of certain hardening chemicalsto make theasphalt sufficiently rigid not to move within itself and atthe same time t0 leave it sufficiently plastic, so that at coldtemperatures when hardening takes place, there will be sufficientflexibility to avoid the breaking and disintegration of the surface.rlhese mixtures, however, have not yet proven efficient to remedy theevil.

l have therefore in my present invention provided a pavement wearingcourse construction, whereby. the axis of movement within the body ofplastic material is so raised as to permit it to be negligible in anas'phaltic or bituminous top course of sufficient thickness to retainlits volatile oils ands proper longevity and utility as a pavement.

ypavement may be laid upon worn-out concrete pavement, which has to bere-surfaced, or upon water-bound macadam base, rolled gravell base, orbituminous mixture base, or any other bases of sufficient stability toact as suchl l shall describe two slightly diEerent methods ofconstructing my pavement. These methods involve the same general thoughtand principle and produce a pavement wear course accomplishing mypurpose of so anchoring the upper and lower layers of the body ofplastic surface material that the axis of movement is practicallyeliminated or becomes a `negligible factor. y

According to the first method, as shown in Figure l, li place upon thebase 10 a course A of asphaltie concrete or bituminous mixture,containing standard materials, for which l suggest, for example,approximately seven percent of pure asphalt cement, fine sands, and hardcrushed rock or stone 12, sized from one to one and one-fourth inches ingreatest dimension.

The mixture may be placed on the base i while hot to a uniform thicknessof not less than approximately one inch, so 'that it will beapproximately three-fourths of an inch in After raking, T place on topof this layer,

sheets of expanded metal (steel) reinforcement 14 having openings ofapproximately two to two and one-half inches in their long dimensions(inside measurement) and approximately one to one and one-half inches intheir short dimensions (inside measurement).

This mesh can be readily placed by hand and the edges merely interlockedto makea continuous mat or mesh over this whole lower course'ofasphaltic material.

As soon as possible another similar course or layerv B is placed abovethe bottom course with the mesh thereon. The whole mass vis then rolled.The rolling causes the stones in the mixture to protrude up from thebottom course or project down fromthe top course or both through themesh of steel, thereby in-' terlocking themselves in the upper and lowerportions or layers of asplialtic material. through this semi-rigid steelcenter plane, and thus tying the whole mass completely and effectivelytoget er, and raising the axis of movement, which would ordinarily beabout the level of the steel to somewhere near the top ofthe inch overand above the steel, where A it will be negligible. A

.Thus in Figure 2, T have shown the pavement at the left, before rollingby the roller 16, and at the right, after rolling. The pavement beforerollingis also illustrated in Figure 5 and after rolling in Figure 6.

- The relative size of the openings 'in the mesh and of the stone shouldbe such that when the compression of the pavement hasoccurred and thestone pressed closely together in the mass, there can be no movement ofthe upper portion of 'the pavement sufficient to cause harmful resultsbecause of the anchorage afforded by the arrangement of the stone withrelation to the mesh and the asphaltic mixture above and below it.

Upon final completion, Ait would only be necessary to use a paint coator a squeegee coat of hot *asphalt cement over the surface and sand itdown by brooming hot clean sand over the paint or seal coat of asphalt.-

The result under traffic afterv the original seal coat has been worndown is a monolithic surface containing high stone content meeting theabrasion and Wear, thoroughly keyed toa semi-rigid steel mesh anchoredin the center ofthe surface slab by larger stone protrudingboth upwardand downward throughv the mesh. Thus there would not be permitted Y anysubstantial movement of any one stone under traiiic to move itfurtherthan a small prifjtion of the mesh opening in the steel it- Se 7llnasmucht as the stone would be approximately of a size to wedge itselfinto the mesh opening, it Nwould be impossible for the stone to move toany degree to form in the plastic surface rolls or surface imperfectionsto any extent which would be noticeable to traffic.

"taining no large aggregate, of such athickness that if rolled it willnot be less than three-fourths of an inch in depth. (Figure 7.)

This should be raked or fluifed to a true contour.

After raking, there is placed on this layer of sheet asphalt, expandedsheet metal 14, suchas above mentioned.

After placing the reinforcement in position, another similar layer ofasphalt mixture 2O is laid on the mesh and lower course, approximatelyone inch thick. This should be flufed and may be lightly rolled or not,as practice will denote. In either case, While the mass is ready foreither preliminary or fina-l rolling, as the case may be, crushedangular hard stone or rock 22 of approximately from one to one andthree-fourths inches in largest dimensions, preferably previouslytreated with naplithene or light oil to clean it, is cast evenly overthe surface of the mass.

Immediately thereafter, the pavement is rolled with heavy rollers andthereupon the stone in the completed wear course will form a hard almostrock top surface and the larger stones or rocks will be forced down intoor through the steel mesh for anchoring the bottom and top layers andsteel mesh and thoroughly locking them together in the same way as hasalready been mentioned.

It may perhaps be stated that natural rock asphalt or cold preparedmixes may be used for my pavement as well as any of the mixtures nowused or to be developed in practice.

Tn the completed product, if the mesh and stone are of the proper sizeand the two layers are of the proper thickness, the normal movement ofthe body of material withinitself will be eliminated.

When this result has been'accomplished, no anchorage of the completedtopv coat or cou'rse to the base is necessary. For if there is nomovement in the top course itself, there will be no movement of thebase. This is of particular importance in laying my pavement as a topcourse on old concrete pavements which have smooth surfaces and to whichit would be difficult to anchor the top or wear course.

The reinforcing should preferably be substantially fiat or in sheets sothat'it will not interfere with the raking and fluffing.

It will be noted that my pavement may be made of materials, which aregenerally and readily available and laid with the equipment lin myclaims, l intend by the use o f asphalt or asphaltic bitumin orbitumlnous to include any plastic paving material 'adaptable for thepurpose, and normally having movement within itselt.` Likewise by' meshreinforcing, I would include any material'suitable for my object.

ll claim as my invention:

1. A pavement comprising a suitable base and a Wear course thereoncomprising a lower asphalt layer, a metal mesh reinforcing laid thereon,an upper4 asphalt layer, said wear course having crushed hard rockprojecting into and through the meshes of the reinforcing, the rockbeing of such size relative to the thickness of the course and the sizeof the openings in the mesh that whenthe wear course iscompressed therock will enter and project through and nearly lill the meshes so thatthe twolayers and reinforcing will be thoroughly anchored together.

2. A wearing course for a pavement hav ing a lower asphaltic layer, asemi-rigid mesh anchoring element thereon, an upper asphaltic layerresting upon said lower layer and covering said anchoring element, saidlayers having aggregate therein projecting through the meshes of theanchoring element, said aggregate being of a maxnnum 'd1mens1on\ greaterthan the thickness of either layer and the size of the meshes bein@ suchas lto receive the aggregate so that the aggregate will havesubstantially no horizontal movement there- 3. A pavement comprisingacourse of asphaltic material, angular rock aggregate in Said course ofa largest dimension greater than half the thickness of the course, andmeans in the course substantially spaced from the top and bottom thereoffor permitting movement of the rock vertically inthe course when thecourse is compressed by trac or otherwise and for substantiallypreventing the movement in a horizontal direction of that'portion oftheaggregate adjacent to it.

4. In a pavement wear course, a layer of asphaltic material, semi-rigidmesh anchoring means thereon, a top layer of asphaltic material, andhard ag regate in/said course, project-ing through the meshes of theanchor-v ing means, and of a size relative to such meshes, tosubstantially fill them. f

Des Moines, llowanluly 30, 1928.

LEON llt. MACKENZIE.

